The present disclosure relates to an alkaline battery including a safety valve that operates upon abnormal rise in the internal pressure of the battery and particularly relates to a structure of a sealing unit for sealing an opening part of a battery casing.
Referring to a general cylindrical alkaline battery, a positive electrode mixture 102, a gelled negative electrode 103, and a separator 104 are put in a bottomed cylindrical battery casing 101 together with alkaline electrolyte, and the opening part of the battery casing 101 is sealed by a sealing unit as an integration of a negative electrode terminal plate 105, a negative electrode current collector 106, and a gasket 107, as shown in FIG. 6A.
The gasket 107 includes a boss part 107a through which the negative electrode current collector 106 passes, an outer peripheral part 107b in contact with the opening part of the battery casing 101, and an annular part 107c arranged between the boss part 107a and the outer peripheral part 107b, and thin part 108 serving as a safety valve is formed at a part of the annular part 107c. Upon abnormal rise in the internal pressure of the battery, the thin part 108 is broken to release gas generated in the battery outside the battery through a gas hole 109 formed in the negative electrode terminal plate 105, thereby preventing the battery from being burst.
In the case where short-circuit occurs in a state, for example, where a plurality of batteries are connected to each other in series, the short-circuit current causes abrupt temperature rise of a battery itself to soften the gasket 107, which is made of resin, by the high temperature heat and to deform it by the pressure of gas generated inside the battery. In this state, if the annular part 107c of the gasket 107 is bent and extended fully to be in contact with the negative electrode terminal plate 105, as shown in FIG. 6B, the thin part 108 cannot be broken to invite ineffective operation of the safety valve.
To tackle this problem, Japanese Unexamined Patent Application Publication 9-7572 proposes a technique for securely braking the thin part 108 even if the annular part 107c is extended fully due to temperature rise in the battery by providing a blade-shaped protrusion opposite the thin part 108 around the negative electrode current collector 106.
Although this technique exhibits an effect of effectively operating the safety valve by securely breaking the thin part 108, the structure of the negative electrode current collector 106 becomes complicated to invite poor mass production and an increase in cost.
Another technique for readily breaking the thin part 108 even when the annular part 107c is extended fully is shown in FIG. 6C. Namely, the boss part 107a is made long to separate enough the annular part 107c from the negative electrode terminal plate 105 in advance so that the thin part 108 is securely broken even when the annular part 107c is extended fully. This realizes an alkaline battery including a safety valve that can effectively operate without inviting structure complication of the negative electrode current collector 106 and the gasket 107.